Orbital Forcing of High Elevation Meltwater Events along the Periphery of East Antarctica

Abstract:

Detailed studies of surface processes and landforms in periglacial environments have proven successful in unraveling the timing and duration of small-scale temperature shifts. Here, we use alluvial fans in the high elevations of the McMurdo Dry Valleys (MDV) of Antarctica as a novel proxy for climate change in the MDV. Alluvial fan depositional events require sufficient melting of the alcove snow (or ice) to enable sediment transport. Under current climate conditions the alluvial fans appear inactive, as there exists insufficient energy for adequate snowmelt. Hence, fan activation suggests times when climate conditions favor meltwater production (i.e. elevated temperatures). Our study reconstructs the depositional history of five high-elevation alluvial fans in the MDV by dating individual sedimentary units using optically stimulated luminescence (OSL). Ages of deposition appear clustered with two groupings in the Holocene and one cluster of deposits slightly older (~14-16ka). We identified high-elevation alluvial fan deposition is sensitive to long duration, low intense summers consistent with previous studies showing increase in cumulative positive degree days to be the primary driver for the terrestrial ice sheets and a warmer Antarctica. Alluvial fan deposition also occurs with short, high insolation summers; a forcing that is secondary or possibly lost in ice sheet or MDV alpine glacier fluctuation. The discovery of repeated high-elevation inland warming evident by meltwater events in the Holocene is unexpected when compared with the nearby geomorphic features including buried ice, rectilinear slopes, and paleosols that appear unmodified for millions of years. We are hopeful the inland alluvial fans will provide controls into the precise climatic conditions required to support surficial melting of the nearby East Antarctic Ice Sheet during times of high insolation or Quaternary interglacials.